Most household gas boilers employ a semi Bunsen burner due to stable inflammability. This semi Bunsen burner mixes some air (primary air) supplied from a blower with gas fuel in advance and supplies the mixture to a combustion unit to form a flame. The semi Bunsen burner supplies the rest of the air (secondary air) supplied from the blower to a flame forming part, thereby inducing complete combustion.
To prevent harmful emissions (e.g. CO) from being excessively discharged from such a burner, the output of the burner is generally required to be less than 2,000 kcal/h. In this case, when the output per burner unit is designed to be low, many burner units should be installed to meet the maximum output required from the boiler. As such, the overall volume of the boiler is increased.
To overcome this problem, a premix burner characterized by a small volume, high load, and low NOx has been used. However, the premix burner has difficulty in control because the range of an air ratio for stable combustion is narrow.
A high-load burner based on a concept of a lean-rich burner adopting advantages of the aforementioned burners has been developed and used. The lean-rich burner is designed so that flame units in which excessive air is burned on one side and flame units in which excessive gas is burned on the other side are alternately provided. In the burner having this structure, a mixed gas ejected from the two types of flame units participates in mutual combustion, so that stable high-load combustion and low NOx combustion can be carried out by the burner having a small volume.
Most lean-rich burners are designed in the form of a dual gas pipe (in which one gas pipe is used for an air-rich mixture and the other gas pipe is used for a gas-rich mixture), and thus have a complicated structure and a large number of parts, which leads to an increase in manufacturing cost.
These lean-rich burners have the same basic structure as a burner shown in FIGS. 1 and 2.
FIG. 1 is a plan view showing a burner unit for a conventional gas burner, and FIG. 2 is a front view showing the burner unit of FIG. 1.
The burner unit is constructed so that a burner body 10 having main flame holes 11 formed in a top face thereof is coupled with side plates 20 having auxiliary flame holes 21 that are formed between the burner body 10 and the side plates 20. The side plates 20 are coupled to the burner body 10 by welding. Each side plate has a plurality of weld spots 30 at regular intervals in a lengthwise direction thereof.
In this manner, when the burner body 10 and the side plates 20 are coupled by welding, the number of manufacturing processes is increased, and thus the cost of production is increased.